The reasons may be very different.

(1) What is the size of the working gap I use? For larger working gap (100 to 200 microns - roughing), the purge side more "purified" as the output side, ie poorer ignition conditions and a higher concentration of the contamination on the output side.

(2) How well did the flushing optimized? In the arrangement shown there is no real lateral gap.

As a small Hife I can not make just one article in German available.

Best regards

Hans-Peter

I think the flushing pressure is more intensive at side than the other. This then result higher wear at the side of flushing. This would also depend on the material type.

Thanks.

Dear Vishal

The problem with side flushing is that wear debris removed at the entry side gets flushed to the output side. As a result the electrolyte at the entry is relatively pure and has ideal conditions for material removal. As the electrolyte goes through the flushing channel the contamination with wear debris increases that makes the path to be more conductive which will reduce the material removal rate. It will form arc between the wear particle and tool rather than between the tool and the work material. That would explain the reason for higher tool wear rate. To take care of such eventualities, a number of other flushing methods are suggested and used depending upon the geometry of the work piece you are interested. See pp 332 – 335 from the book link given here.

Book Manufacturing Technology, Vol. 2 Metal Cutting and Machine Tools

Could be electrolyye

I think we speak of the sinking-EDM, that is, we always use hydrocarbons, so that electrolytic effects can be excluded. Of course, the pressure difference is the cause of the uneven distribution of remove-contamination, but the altered concentrations of contaminants leads to abnormal discharges or arcs. These abnormal discharges should also be excluded by the process control, i.e. I can only partially rely on these types of discharge as a cause of increased wear.

In most articles to wear the flow rate is therefore defined as a process parameter.

Our results show that due to the lower contamination in the flushing area have discharges longer ignition delay. Characterized the anodic removal in relation to the cathode and the greater removal discharge is amplified on the anode.

Whether the dielectric is cracked, should be answered in the negative, according to studies of the dielectric used. Would it be the case, then the dielectrics could not be used so long. In the years 1980-90 was examined in particular whether toxic fractions occur - no.

Now again to the carbon layers to occur at the anode. The main cause of these layers are too many authorized abnormal discharges (eg arcs). These abnormalities can occur if

- Is not achieved  process stability (process parameters, process control);

- Process analysis is not adequate (excluding the abnormal discharges);

- Incorrect flushing (uneven distribution of the contamination in the gap).

The outlined in the question lateral flushing is not really typical and is used only in exceptional cases.

My opinion is the following: in the flushing side, the dielectric are pure. In te opposite side, the wear debris resultant from EDM process acumulate. In the flushing side the spark jump betwen electrode and material. In the opposite side the spark jumps between the electrode and the wear debris, This is the reason because the wear is inhomogeneus. One possible solution is to introduce the dielectric fluid trough the electrode. In this case, the wear will be homogeneus.

Thank Prof Krahmer for your response.

But what  observed from research articles that the same issue can be observed in the case of through flushing also. I am attaching a figure that has been published by Ozgedik and Cogun in their research work entitled "An experimental investigation of tool wear in electric discharge machining" published in IJAMT in 2006. In this work, they used through flushing to study the tool wear aspects. They too observed similar wear characteristic (i.e. high wear at the fluid entry side - which is along the inner diameter of the tool electrode and vice versa.

In the sinking EDM, taper side walls is normal, but when the dielectric flushing is through the electrode, the wear should be homogeneus, because the flushing zone is in the center of the electrode. In this case, the dielectric flushing in homogeneus manner.

Basically centrally flushed arrangements are always better with a uniform distribution of particle-removal only occurs when the workpiece shape is symmetrical. It is also important to distinguish between the flushing pressure and flow rate. A high flushing pressure does not necessarily produce better process conditions. A high flow rate means but that is the "dilution" of contamination is higher and thus better breakdown conditions are set.

The configuration shown above is just only a partial good solution, in which you scored very different wear conditions on a tool. For scientific studies quite interesting, but in practice only a "last resort". In practice, an oscillating movement of the electrode is more efficient (wear), the gap a substantially higher pressure (uniform) is achieved in the working gap and regenerated completely and uniformly. The oscillating electrode arrangenment has a time constant in the millisecond range and should not be eroded in the complete time range productivity is of course somewhat reduced. So it is before answering the question, what is my primary goal, high productivity with restrictions on the machining accuracy or high machining accuracy with reduced productivity. In micromachining you tend mostly to the latter.

Regards

Hans-Peter

The answer to this question is the same that for the use of a tool and workpiece in same material.

The electrical potential.

Oops, how did I understand this response?

I think that the EDM with the same electrode materials is not unlike different materials. The energy conditions of the cathode and anode caused by the mechanisms of the ignition process.

Of course, the "pure" area, the firing condition is deteriorating and this is also a reason for the higher wear because the wear caused shares in the proximity of ignition. From the potential fundamentally changed nothing, ie the electrodes retain their potentials. With the increasing gap region the effective electric field strength decreases.

Or do you think Prof. Marafona something else?

Best regards

Hans-Peter

Infact I did not understand the response given by Prof. Marafona.

Sir, can you please explain your response?

Dear Schulze

The electrical potential changes in the gap at least the voltage control value of servomecanism and this change is at high level of potential (anode), so the receding in the boundary of the  crater  of erosion occurs in the steel tool and not at the bottom (cathode) of the electrode because the electrical potential is near the reference (zero) meaning that the decrease in the electrical power does not affect it. The cathode erode more than the anode.

So, if you use lateral flushing you are changing the electrical potential in the tool radius (dielectric flushing), and so you put the potential to zero  in this side of the tool. So, you create a cathode in this side of the tool that goes to erode more because the electrical potential do not decreases (near reference, zero)  and "more energy" is used because there is not loss, thus in the other side of the tool will occur the effect caused by the loss of power in the reference side.

I hope to clarified your doubt...

Best regards,

José Duarte Marafona

Dear Marafona

Perhaps we should agree that there are several effects that cause a different wear behavior between flushed and non-flushed side of the electrode assembly.

With the purge I change once no potential at the electrode surfaces. An exception is when gas bubbles enter into the dielectric, which settle on the surface and change the potential of the double layer. This potential is verschwindent but small compared to the applied trigger voltage, ie Maximum formation of additional carriers may be impaired.

Now to the zero reference potential. In most cases, mass (device housing or the workpiece), and zero potential is equated, resulting in Erode to major problems, because the zero potential "floats". Therefore, all voltage measurements with a differential probe must be made. Do we now the "true" analyze voltage curve, then the time share is particularly interesting to the achievement of the spark burning voltage for wear analysis.

The gap voltage recordings as we can now direct over time, then we can see if all discharges are sparks, or if there is a change in the number of other discharges (arcs, abnormal discharges). For the measurement of the average gap voltage can I make only one statement, if sufficiently many "false discharges" occur. With an increasing number of failed discharges, the wear increases strongly. Cause include the modified power increases in arcs and abnormal discharges.

But we can also have a less spectacular effect. The discharge breaks off before the actual end of the pulse, and ignites at a time when new, where the pulse is to actually pay off at the anode. Due to the frequent re-ignition of the wear-intensive part of the discharge is increased in percentage, ie greater wear.

Best regards

Hans-Peter Schulze

Dear Hans-Peter

You write

"With the increasing gap region the effective electric field strength decreases."

Do you believe that the gap increases also during electrical discharge or not? There is not an evaporation of material during electrical discharge?

So, you must think about your statement and the electrical potential variation.

Off course there are many parameters that affect the tool wear with and without flushing, howver one must identify the main cuase and in my opinion that is due to the electrical potential change.

Best regards,

José Duarte Marafona

DearJosé Duarte

I do not understand where the gap a potential change to take place.

Let us go systematically, then the double-layer potential could change if other materials (layers, gas, ...) deposited on the surface itself. These changes in the potential are maximal in V range and are of no interest at 200 to 300 V ignition.

Since the zero potentials are almost all systems on the machine mass, they can be altered by interference. These changes can be up to several volts, ie I want a control to measure the potential difference between the anode and cathode, then I have to compete with a Differetial probe.It is also possible to measure against a zero-potential electrode.

Can be guaranteed that the anode potential is zero, then there is moderately process for the cathode only four states. Also zero in the interpulse period, the ignition voltage, electrical breakdown voltage to the spark burning and clearing the discharge to zero potential. The oscillations on the burning voltages are given by the movement and expansion of the discharge. If the discharge channel tear off, the voltage falls naturally to zero. Similarly, the voltage increases again when the channel re-ignites. The means  that with the spark burning voltage of the voltage drop across the working gap is determined only by the discharge channel (channel + plasma gas bubble + interfaces).

The only potential shift (cathode in the normal case) there during the rise time of the ignition voltage and the breakdown of time. At these times, the main effects of wear to take effect. If they think this potential shift, that's correct.

In principle ma can imagine that in the gap a "homogeneous" exists electric field inhomogeneities that at specific surface structures. This stubbornness doors will not change if the "one-sided" purge. Where continuously "clean" dielectric, since the conditions for the firing and for the stability of the channel is critical, ie Pulse can leave early and a variety of new ignitions, ie greater proportion of wear-times and usually less erosion. At the "bad" purged end of the assembly to focus the carry-particles and thereby fulfill the conditions that the pulses earlier ignite (low ignition delay) and "electrical conductivity" of the gap region are stable through the slightly better. But be careful! the risk of arcing and abnormal discharges increases.

Always include a variation of the potential, I think my work in the gap. There compress or dilute the equipotential lines, which is equal to the mean increase or decrease of the electric field strength. We can also talk personally about each parts in the ignition.